Method of making die blocks for forging turbine blades



Jul 22, 1930." R. c. ALLEN 1,770,964

METHOD OF MAKING DIE BLOCKS FOR FORGING TURBINE] BLADES Original Filed-6- 1924 2 Sheets-Sheet l l o WITNESS INVENTOR RC. ALLEN.

@IVbIM ATTOR N EY July 22, 1930. R. c. ALLEN 1,770,964

METHOD OF MAKING DIE BLOCKS FOR FORGING TURBINE BLADES Original FiledDec. 3, 1924 2 Sheets-Sheet 2 Fla. .5. Fla. 5.

INVENTOR R.C.ALLEN.. m. M

ATTORNEY .Fatented July 22, 1933 UNITED sTA TEs PATENT orriciz ROBERT c.ALLEN, or swan-Truman,rmvirsYLvANIA; assreivoaro wrisrrneriousn ELECTRIC& MANUFACTURING COMPANY, A CORPORATION or PENNSYLVANIA METHOD OF MAKINGDIE BLOCKS FOR FORGING TURBINE BLADES Original application filedDecember 3, 1924, Serial No. 753,582. Divided and application filed.June 14, 1927. Serial No. 198,852. Again divided and this applicationfiled April 30, 1929. Serial No. 359,304.

This application is a division of application Serial No. 198,852, filedJune 14, 1927, which in turn is a divisionof application Serial No.753,582, filed December 3, 1924.

The present invention relates to a method of making a die block, moreparticularly a die block as described in the first mentionedapplication, which die block is used for making turbine blades coveredin the second mentioned application.

The object of the present invention is to provide an economical methodof making a die block for forging turbine blades having varying bladetip. 1

Apparatus embodying features of my invention. is illustrated in theaccompanying drawings forming a part of this specification in which:

Fig. 1 is a fragmentary sectional View of a turbine rotor and cylinderhaving my improved blading applied thereto;

Fig. 2 is a diagrammatic View descriptive of the motive fluid flowthrough the blades and showing in section a part of the bladesillustrated in Fig. 1 along the lines 22 and 22 of Fig. 1; V

Fig; 3 is an elcvationof one of the blades, drawn to a larger scale thanFig. 1 and show ing in section the varying contour of the blade fromrootrto tip;

Fig. 4 is a plan view of a milling machine with a die block for forgingmy improved turbine blade in process of being formed;

Fig. 5 is a side elevation of the die block shown in Fig. 1 andindicating the direction taken by the milling cutter shown in Fig. 4;

Fig. 6 is an end elevation of the die block illustrated in Fig. 4, drawnto a larger scale and showing the contour of the cut made by the millingcutter in Fig. 1 andthe contour of the cameo member of the die blockemployed in forging the blades;

Fig. 7 is a'view of the milling machine and die block shown in Fig. 4,the position of the die block being altered from the position shown inFig. 4;

Fig. 8 is a side elevation of the die block showing from another Viewthe position of the the block in Fig. 7 and also showing the crosssection from blade root to direction of the cut made by the millingcutter illustrated in Fig. 7;

Fig. 9 is a view similar to Fig. 6 showing the contour of the cutmade'by the milling cutter in Fig. 7, the altered position of the dieblockin Fig. 7 from that shown in Fig. 4, and the contour of'the cameomember of the die block employed in forging the blades;

Fig. 10 is aper spective view of the completed die block and showing thesurfaces of the blade devel-opedrthereby.

In turbines of the multi-stage type actuated by elastic fluid(hereinafter referred to as steam) the blade space between the rotor andthe casing of the turbine increases from the end of the turbine wherethehigh pressure steam is admitted to the exhaust end.

thereof in conformity, more or less, to the specific volume of the steamat the various pressures n the various stages of the turbine.

Thus the blades in the high-pressure end of the turbine are relativelyshort while the j blades in the low pressure end are relatively long. yr

The diameter of the rotor of a turbine plus the lengthof a blade, whichis equivalent to a diameter measured across the rot-or between themidpoints of the blades on oppositesides thereof, is usually referred toin turbine practice as the mean diameter of the blades. The low-pressureblading in large condensing steam turbines has been made, in the past,as long as one-fifth of the mean diameter with a fair degree of eff-iciency. .Thereis, of course, an a ipreciable' difference in peripheralspeed atthe tip and at the base offa blade of this height, the tiphaving a peripheral speed 50% greater than the speed at the base in thecase of a rotor blade, In past designs, wherethe length of the blade didnot exceed one-fifth of the mean diameter, blades of parallel sectionshave been used for the reason that they may be more cheaply produced.Where the blades have been produced by drop-forging, the dies thereforhave been machined by a planing or milling process. lVhere the bladeshave been cutfrom'a solid bar, elther milling or planing operations havebeen employed.

With blades of parallel sections as great as one-fifth the mean diameterin length, there is some disturbance to the steam flow at the tip and atthe base portions of the blade, inasmuch as the blade inlet angle isonly correct at one point, usually at the mean diameter or mid portionof the blade.

In recent turbines it has been found necessary to use blades greater inlength than onefifth of the mean diameter and of higher peripheralspeeds than those employed in the past. For such blades parallelsections can no longer be successfully employed as the centrifugalstresses in the rotor blades are entirely too high for the materialusually employed in making the blades. It has therefore been foundnecessary to taper the blades from base to tip so that their crosssectional area increases from the tip toward the spindle at such ratesthat longer blades may be run at high speeds but with no higher stressesthan when blades of parallel sections are employed.

As the blades increase in length from the high to the low-pressure endof the turbine, the speed of the tips of the moving blades relative totheir root portions increases and the velocity of the motive fluiddischarged from the moving blades, if considered relative to the statoror casing, is, in most practical applications, less at the tips than atthe root portions of the moving blades. Assuming that'the motive fluidleaves a row of moving blades at a constant angle to the side of theblade row from the root to the tip of the blades the difference in speedof the blade at the root and the tip gives a resultant direction, ortrajectory, to the steam leaving the blade row which variesprogressively from the root to the tip, if the direction relative to thestator or casing be considered. Thus, the motive fluid may leave theroot of the blade in a moving row, for example, with a trajectory at anacute angle relative to the stator, while at the tips of the blades thetrajectory of the steam leaving the row may be at approximately a rightangle, relative to the stator or even an obtuse angle, depending ofcourse, upon the blade speed, the steam speed and the exit an glerelative to the side of the blade row.

From the above it is evident that in order to avoid eddying of themotive fluid as it enters the succeeding row of stationary blades theinlet angles of those blades should be such as to correspond with thevarying trajectory of steam leaving the preceding row of moving bladesin the example assumed in the preceding paragraph, the inlet angle ofthe succeeding stationary row of blades should be an acute angle at thebase of the blade varying to approximately a right angle at the tip.Considering the relative motion of the stationary and moving blades itwill be evident that the nest succeeding row of moving blades shouldhave similar corresponding inlet angles.

It is obvious that variation in outlet angles will cause a radialdisplacement of the center of gravity of the steam flow so that specialproblems will be introduced if the outlet angles are varied. Consideringthe foregoing, therefore, it will be apparent that the most efiicientand desirable blade structure is one wherein the exit angles of theblades are constant and wherein the inlet angles vary from the roots tothe tips of the blades in conformity to the varying trajectory of theentering steam.

In order to meet the requirements of a long ta ered blade which mayaccommodate itself to the varying conditions of steam flow through theturbine, the manufacture thereof has heretofore been a long, laboriousand vary expensive process. It has been proposed to forge the blades andto thereafter warp or twist them by means of a suitable tool, in orderto provide suitable inlet and leaving an gles. Blades have also beenmade, rough forged, and the steam passages afterward formed by severalseparate machining and hand processes. Either of these methods isobviously expensive and attended with many difficulties.

In accordance with the invention set forth in the above mentionedapplication, Serial No. 753,582, I provide a relatively long, taperedblade, each surface of the port section of which is defined by planesurfaces and cylindrical'or curved surfaces, the axes of which divergelongitudinally and laterally of the blade from the tip to the rootthereof, and which provides a constant leaving angle and a varying inletangle from tip to root of the blade in accordancewith varying conditionsof steam flow in the turbine.

In accordance with the present invention, I provide a method of making adie block for forging blades of this character. The cylindrical orcurved surface of one of the die block members, preferably the cameomember, is out along a straight line which is inclined to the cameomember. The intaglio member may be made of uniform cross section. A dieblock is thus produced for forging the blades, whereby blades of thegreatest eiiiciency may be produced at a minimum cost, and which requireno twisting or warping to accommodate varying conditions of steam flow.

Referring now to the drawings for a better understanding of myinvention, I show in Fig. 1, at 10, a fragment of a turbine rotor and at11 a fragment of a cylinder. At 12 is shown a row of moving bladescarried by the rotor 10 and at 13-13 rows of stationary blades carriedby the cylinder 11. The rows of blades 12 and 13 are of parallel sectionas they are of lesser height than rows 16 and 17 following and thereforemay not require the tapering or working for the reasons stated above.They are followed bymoving rows of tapered blades1616 and stationaryrows of tapered blades 1717, said blades being made in accordance withmy invention. The direction offlow of steam through the blades is fromright to left and may be better understood by reference to Fig. 2,wherein a typical steam flow condition through rows 13, 16 and 17 isshown.

In Fig. 2 the blade sections in the upper part of the figure representthe stationaryv rows of blades 13 and 17 and the moving rov. 16 alongthe line 22 of Fig. 1', while the lower blade sections represent thesame rows along the line 22* of Fig. 1. lllccon'ipanying the rows 13 and16 are velocity diagrams in which Vs represents steam velocity, which isconstant from the root to the tips of the blades; V represents bladevelocity along theline 2 2 of Fig. 1; V represents blade velocity alongthe line 2'-2 of Fig. 1; T and T represent the trajectory of the steamleaving a blade row relative to the succeeding row of blades along thelines, 22 and 22, respectively, of Fig. 1. The ankle '6 represents theleaving angle of the steam from each row of blades, which angle isconstant throughout the blade length for both the stationary and movingblades. The varying trajectory T and T is determined by, and is acomponent of, the leaving angle of the steam relative to the blade row,the velocity of the steam and the velocity of the moving blade row atthe point considered. The angles made by T and T with the side of theblade row determine the'inlet angle of the next succeeding row of bladesatthat point. Inasmuch as the blade velocity along the line 22 is muchgreater than the blade velocity along the line 2-2 the inlet angle alongthe line 22 as determined by the trajectory T is 1' uch greater than theinlet angle along the line 22' as determined by T in order to avoiddisturbanc s in the steam flow as hereinbefore pointed out.

Referring to Fig. 3, I show in further detail a blade made in accordancewith my invention. In this figure 18 represents the port, or workingsection, of the blade and 19 the root or holding section which may be ofany form known in the art. Sectional views of the port section 1.8 areshown in 21,

22, 28, 24 and 25, said sectional views show ing the inlet-and leavingangles of the blade at the respective points selected. It'will be notedthat the port section 18 of the blade decreases in cross section fromthe root to the ti) thereof and that the leavin an le 6 is l is.

constant from the root to the tip. The inlet edge of the blade makes anangle with the side of the blade row as shown at ca, 0. or, a and a saidangles being relatively small near the root of the blade. and increasingtoward the tip in order to accommodate the surface 51 define theback ofthe blade.

varying trajectory of the steam from the next preceding row of blades asshown in Fig. 2 and prevent disturbances in the steam flow. Inaccordance with my invention the blade is so produced that the inletangles increase progressively from the root to the tips of the bladesasma-y best be understood by reference to the method of making the bladewhich will now be described.

In Fig. 4, I show a milling machine 27 which may be driven by anysuitable means as by a belt pulley 28. Mounted upon the machine bed is ablock 29 to be machined for forming the intaglio member ofthe die blockwhich I employ in forging the turbine blades. A milling cutter 31 iscarried by journal bear ings 32 and 33, the latter being fitted toguides and 36 so that theymay be movedback Feed and forth in the cuttingoperation. mechanism for the milling cutter 31 is associated with thebearings 32 and 33,-such for example, as sets'of beveled gears at 37 and38, feed screws 39 and 40, a drive shaft 42 and a hand-operating-wheel48. e

In the operationillustrated in Fig. 4 the block 29 is placed at rightangles to the cutter 31 and the cut is made straight througl'i the faceof the block as indicated bythe dotted line 44 in Fig. 5. The contour ofthe cut which I have found desirable for reaction blades is illustratedin Fig. 6 and comprises a cylindrical surface 45 supple1nented by a flattangential surface 46. The surfaces 45 and 46 definethe contour of thecameo member of the die block which is illustratedat 47 andconsequentlythe contour of theconcave or workingface of the blade. Theflat surface 46 is at the leaving side of the blade,while the curvedsurface 45 is at the inlet side. Each of these edges may beprogressively changed from root to tip of the blade in the operationabout to be described iii) and which constitutes one of the most important features of my invention.

Referring to Figs. 7, 8 and 9, I show the next operation inmaking thedie block. In the operation here illustrated, I show a milling cutter 48which makes a cut in the bloclr 29 having a contour as illustrated inFig. 9, comprising a curved surface 49 supplemented by a flat,tangential surface 51. It is to be understood, however, that theparticular contour of either of the cuts illustrated will vary with thearea and'configuration of the required steam passages between adjacentblades. The curved surface49 and the flat In making the cuthereillustrated the block :29 is shifted at one end to one side from theposition illustrated in Fig. 4, and as illustrated by the dotted line 52in Figs. 7 and 9 and also raised at one end as shown at 53,

Figs. 8 and 9. The cutter 48 is now driven straight through the block29, whiohhas been shifted to the position indicated, and in transversingsaid block the right side of the surface 49, as shown in the drawing,approaches and cuts the right edge of the surface l5 considered in thedirection from the blade tip forming portion to the blade base formingportion. In proceeding through the block 29 a different part of thecurved surface of the milling cutter el8 cuts across the curved surface.describing therewith a skew curve, or a curve of double curvature.

As is well understood in the art, when producing an article byforging,it is necessary that a space be left along the inner edges of thestriking surfaces of the die members for the flow of metal. This isnecessary in order to produce an article of definite dimensions. Iaccordingly show spaces 56-56 at each side of the die block toaccommodate the before mentioned flow of metal. These spaces or groovesmay be formed by any suitable process. When the metal for forming theblade is forged, therefore. there will be at each side thereof a fringeof rough metal extending the length of the blade. In the finalcompletion of the blade this fringe is cut by any suitable process,preferably in a straight line along the edges of the blade. Theresultant inlet edge of the blade then is finally resolved into a planecurve, the curvature of which depends upon the curvature of thecylindrical surface 45 and the direction of the cut diagonally acrosssaid surface.

The inlet edge of the blade being defined by a plane-curve extendingfrom end-to-end of the port section 18 of the blade, results in aflattening out of the inlet angle or causing it to become progressivelygreater from the base to the tip as will be more particularly describedlater. In making the out last described the block 29 is raised at itslower end as indicated at 53 in Figs. 8 and 9. The milling cutter 48 isdriven straight through the face of the block 29 so that the curvedsurface 49 is cutdeeper at the lower end of the block than at the upperend and gradually approaches the curved surface 45 of the cameo member 4as it approaches the top, the two surfaces 45 and i9 thus defining anarea of progressively decreasing cross section from base to top.Referring to Fig. 9 the axis of the surface 49 is indicated at O and theaxis of the surface 45 at X, said axes lying in different horizontalplanes. Upon considering the paths of the milling cutters 31 and d8 indescribing these two surfaces as illustrated in Figs. 4 and 7, it willbe seen that the axes O and X converge longitudinally and laterally fromthe base to the top of the area defined.

In the particular blade heretofore des ribed, which blade represents thepreferred embodiment of my invention, the axes O and X do not, at anytime, intersect, the axis 0 passing beneath and beyond the axis X. It isentirely possible, however, that a blade might be developed in themanner described in which the relative inclination of the two curvedsurfaces 45 and 49 be such as to result in intersecting axes.

In Fig. 10, I show a perspective view of the completed die block whereinthe port section 18 of the blade is lying in the intaglio member 29, theresulting concave surface of the intaglio member and of the blade beingsubstantially conjugate to the convex surface of the cameo member. Thedirection of the inlet edge of the blade with respect to the cylindricalsurface 45 is indicated at 541-. It will be plain that the line 54cutting the curved surface 45 defines an inlet edge for the port section18 of the blade, said inlet edge being such as to present aprogressively increasing angle to the side of the blade row from thebase to the tip. It will be further evident that the two flat surfacesQ6 and 51 cooperate to provide a leaving edge which presents a constantangle to the side of the blade row.

In the foregoing description, the manner of developing the cameo memberl7 of the die block has not been described. Inasmuch as the crosssectional area of the cameo member is constant throughout it may beproduced by any suitable machining process known in the art and whichwill not be necessary to describe here. The intaglio member may also beproduced by other machining processes than milling. For example, theoperations described may also be carried out by a planing process and itis to be understood that the particular machining process thereindescribed is for the purpose of illustration and is that which appearsto me to be the best suited for the operation. It is further to beunderstood that the cooperating surfaces defining the blade may bedeveloped in the reverse to that described; that is, the area defined bythe surface of the intaglio member might be of aconstant cross sectionand the area defined by the cameo might be variable without departingfrom the spirit of my invention.

IVhile I have shown my invention in but one form, it will be obvious tothose skilled in the art that it is not so limited, but is susceptibleof various other changes and modifications, without departing from thespirit thereof, and I desire, therefore. that only such limitationsshall be placed thereupon as are imposed by the prior art or as arespecifically set forth in the appended claims.

In this connection. it is desired particularly to point out that, whileI show my invention embodied in a method of forming a die block forforging a turbine blade, each working face of which is formed along asingle axis for the entire length of the blade, the invention is not solimited, and the claims are intended to cover my invention whereembodied in a method of forming a die blockfor forging any substantiallength of a turbine blade.

WVhat I claim is: r r

1. The method of forming one member of a die block for forging turbineblades, which comprises setting the member at an angle both verticallyand laterally to the direction of travel of a cutter and then moving thecutter in a straight path, relative to the memher, to produce therein acutof the contour of one side of the blade to be forged.

2. The method of forming a die block coinprising cameo and intagliomembers for forging turbine blades, which includes machining one of themembers to form a curved surface having a straight line axis for forming one side of the blade and cutting the other member in straight pathwhich is at an angle laterally to the first mentioned axis to produce acurved surface for forming the other side of the blade. g

3. The method of forming a die block comprising cameo and intagliomembers for forging turbine blades, which includes machining one of themembers to form a curved surface having a straight line axis for formingone side of the blade and cutting the other member in straight pathwhich is at an angle 7 both vertically and laterally to the firstmentioned axis to produce a curved surface for forming the other side ofthe blade.

l. The method of forming a die block for forging a turbine blade havingconcave and convex cylindrical surfaces,- which comprises forming aconvex surface on the cameo member to form the concave surface of theblade,

then cutting the intaglio member to register with the cameo and thendriving a cutter straight through the intaglio member in a directionwhich is inclined both vertically and laterally to the direction of thefirst cut, thereby producing a concave surface for forming the convexsurface of the blade.

5. The method of cutting the intaglio member of a die block for forgingturbine blades which comprises forming a cut of uniform contourlongitudinally of the member, then setting the member at an angle bothvertically and laterally to the direction of travel of a cutter and thenproducing in the member a cut of the'contour of the convex a side of theblade to be forged.

6. The method of forming a die block for forging a turbine blade,comprising cutting a cameo member to form a convex cylindrical surfaceof uniform cross section, and driving a cutter straight through theintaglio member to produce a concave cylindrical surface, the axes ofsaid surfaces being in- ROBERT C. ALLEN.

clined toward each other and non-intersecti mg.. V

7. The method'of cutting a die block for forging a turbine blade havingconcave and convex cylindrical surfaces whose axes diverge, whichcomprises forming a' cameo

